mainspring
spiral torsion spring of metal ribbon used as a power source in mechanical watches, some clocks, and other clockwork mechanisms
en-US/ˈmeɪnˌspɹɪŋ/
en-GB/ˈmeɪnspɹɪŋ/
spiral torsion spring of metal ribbon used as a power source in mechanical watches, some clocks, and other clockwork mechanisms